1. Field of the Invention
The present invention relates to a phase discrimination type electrostatic capacity detector. More specifically, the present invention relates to a miniaturization of the detector in which a one-side electrode plate including transmitting and receiving electrodes and another-side electrode plate including a coupling electrode are disposed relatively movably in a confronting relation, with a power supply of different phases applied to the respective transmitting electrode elements to discriminate the phase of an electric signal induced on the receiving electrode for detection of a change in electrostatic capacity coupling therebetween. Such a detector is applicable to a displacement detector and a length measuring device.
2. Description of the Prior Art
Referring to FIGS. 10 to 13, a prior phase discrimination type electrostatic capacity detector is illustrated in general construction.
As illustrated in FIG. 10, the phase discrimination type electrostatic capacity detector comprises a one-side electrode plate 10, a other-side electrode plate 20, a power supply 30 and a detector circuit 40.
The one-side electrode plate 10 includes a transmitting electrode 11 composed of a plurality of transmitting electrode element units (transmitting electrode elements 11a to 11h) and a receiving electrode 17. The transmitting electrode elements of the same phase (11a, 11a, . . . for example) are connected to coupling leads 13 through extension leads 5 and further connected to the power supply 30 through a flexible wiring 16, respectively, as illustrated in FIG. 12.
The receiving electrode 17 is connected to the detector circuit 40 through an output lead 18.
In contrast, the other-side electrode plate 20 includes, as illustrated in FIG. 13, a plurality of coupling electrodes 21 and a plurality of earth electrodes 22 mutually short-circuited by a short-circuit pattern 23, both being alternately arranged. Each coupling electrode 21 extends in its length over four transmitting electrode elements (11a to 11d, for example) and in its width from the transmitting electrode 11 to the receiving electrode 17.
Both electrode plates 10, 20 are disposed in a confronting relation, as illustrated in FIG. 11, and movable longitudinally (the face to the back of FIG. 11).
Herein, AR designates an electrostatic capacity coupling area. The respective leads 5, 13 are provided in a connection area other than the electrostatic capacity coupling area AR and connected to the flexible wiring 16.
The power supply 30 includes, as illustrated in FIG. 10, an oscillator 31 and a signal generator 32 for generating a plurality (8) of signals different in phase from each other. The detector circuit 40 includes an integrator 41, a comparator 42, an edge detector 43, a phase difference detector 44 for phase discrimination, a counter 45, and a display 47.
If the one-side electrode plate 10, the power supply 30, and the detector circuit 40 are mounted on a body of a dial gauge type length measuring instrument and the other-side electrode plate 20 is mounted on a spindle attached slidably to the body, the amount of displacement of the spindle can be read on the display 47.
Such a prior phase discrimination type electrostatic capacity detector is advantageous in reduced power consumption, high resistance to disturbance, and high resolution, compared with a photoelectric type detector and the like for example.
In such a prior detector, however, the same phase transmitting electrode elements (11a, 11a, . . . , for example) are connected to the same coupling lead 13 through the respective extension leads 5, as illustrated in FIG. 12. In detail, as illustrated in FIG. 14, the extension lead 5 is disposed on a substrate 19 of the one-side electrode plate 10 as being the same level as the transmitting electrode element, and the respective coupling leads 13 are disposed above the extension lead 5 through the electrical insulating layer 1. Therefore, each extension lead 5 is connected to the coupling lead 13 through a connection terminal 6 which is yielded by forming a through-hole 3 through the electrical insulating layer 1.
Herein, as illustrated in FIG. 15, if the widths of the coupling lead 13 and the connection terminal 6 are assumed W and D, respectively, then the width D falls within 0.1 to 0.2 mm owing to the restriction of the through-hole 3 in view of processing of the same although the width W suffices to be 0.03 mm on the electrical characteristics. The former width D leads in case of eight phases to a size L needed to construct the overall coupling leads 13, which amounts to 0.9 to 1.9 mm that is excessively large compared with the width W (0.03 mm) of the single coupling lead 13, preventing the whole of the detector from being miniaturized.
Such a prior detector is therefore not applicable to a handy small-sized length measuring instrument and the like, for example. Even though the size of the through-hole 3 is reduced, difficulty of processing thereof produces bad yield and makes the device costly. Formation of many through-holes 3 is not only expensive in itself but is liable to cause broken wiring. Further, since the connection area between the coupling lead 13 and the extension lead 5 is located on the side of the transmitting electrode 11, the lateral size of the one-side electrode plate 10 is further increased and prevented from being miniaturized also from this point of view.
On the contrary, in order to make such a prior phase discrimination type electrostatic capacity detector more stable and accurate in characteristics thereof, it is sufficient to make a relative positional relation between both electrode plates 10, 20 accurate.
To solve this, the present applicant has previously proposed a detector system in Japanese Utility Model Application No. 63-199690 (not laid-open yet), for securely increasing the stability of electrostatic capacity coupling between the coupling electrode 21 and the transmitting and receiving electrodes 11, 17 or improving parallelism therebetween more positively. The detector system comprises the receiving electrode 17 composed of a couple of the receiving electrode elements 17A, 17B, between which the transmitting electrode 11 is interposed, and parallelism detector means 50 composed of couple of integrators 51A, 51B connected to the receiving electrode elements, respectively, a comparator 52 and a meter 53, as illustrated within FIG. 3 partially. Herein, designated at 46 is an adder.
Such a detector, which includes the couple of the receiving electrode elements 17A, 17B incorporating the transmitting electrode 11 therebetween, however, has problems that the device becomes large-sized and it is difficult to be executed technically and uneconomical to process the device.
Specifically, the respective extension leads 5 and the coupling leads 13 are difficult in their formation as patterns on the side of the transmitting electrode 11 and outside the electrostatic capacity coupling area AR, as illustrated in FIG. 11. Accordingly, they must be laid to go around the transmitting electrode 11 and the receiving electrode 17 (17A, 17B) for away therefrom longitudinally, as illustrated in FIG. 16. Thus, the one-side electrode plate 10 is not only excessively long and costly, but also limited in its application such that it can not be assembled into a handy measuring instrument, for example.
To form the coupling lead 13 within the electrostatic capacity coupling area AR, a structure may be thought as illustrated in FIGS. 17 and 18, wherein a stepped portion 19b is provided in one side end 19a of the substrate 19 which forms the one-side electrode plate 10 for connection of the flexible wiring 16 utilizing the recessed portion 19b. In the structure, however, since the substrate 19, which is made of a glass plate, must be processed in itself to form the stepped portion, a technique to process it is severe together with heavy economical loading and insufficient stability. Furthermore, if there is any dimensional error and bonding failure on the flexible wiring 16, the flexible wiring 16 is protruded into a gap between the coupling electrode 21, and the transmitting electrode 11 and the receiving electrode 17 to cause reduction of the reliability of the device such as impossibility of a smooth relative movement thereof and occurrence of unstable signals.